High-power optical microscopes can use objectives with large numerical apertures (NA) resulting in high resolution imaging. In the case of oil or water immersion objectives these NAs can exceed 1.0. In any optical system, the first aberration that causes loss of signal and resolution is spherical aberration. Spherical aberration is the artifact in an imaging system caused by the inability of the optical system to focus axial and off-axis light from a point source to a single point. Modern objectives are highly corrected for spherical aberration, using multiple lens elements to eliminate the effect. However, these objectives are corrected only for a single ideal situation (e.g., for a specific cover glass thickness for samples on the cover glass). In practice, moving deeper into the sample introduces spherical aberration and is usually the limiting factor in deep imaging with these objectives. This is true especially in the case of multi-photon microscopy, which is intended for deep imaging, the sample of interest is rarely in the objective's ideal location.